1. Field of the Invention
The present invention relates to a control circuit for a power converter, and more specifically, to a switching control circuit for switching mode power converters.
2. Description of Related Art
Various power converters have been widely used to provide regulated voltage and current. For the sake of safety, an off-line power converter should provide galvanic isolation between its primary side and secondary side. When a control circuit is equipped at the primary side of the power converter, an optical-coupler and a secondary-side regulator are needed to regulate the output voltage and output current. The object of the present invention is to provide a switching control circuit for controlling the output voltage and the output current of a power converter at the primary side without using the optical-coupler and the secondary-side regulator. Furthermore, the technology of frequency hopping is introduced where the switching frequency of the switching signal is spread and thus the EMI (electric and magnetic interference) is lowered. Therefore the size and the cost of the power converter can be reduced.